Image forming apparatus with laser scanning components positioned for enhanced compactness

ABSTRACT

An image forming apparatus includes plural photosensitive members, a scanner unit for scanning the photosensitive members, and a fixing unit for fixing toner images. The scanner unit includes a rotatable polygonal mirror for reflecting laser beams emitted in correspondence to respective photosensitive members, reflecting members for reflecting the laser beams, and a box for accommodating the polygonal mirror and the reflecting members. The box includes plural outlets for the laser beams. Of the reflecting members, first and second reflecting members reflect laser beams toward corresponding first and second outlets respectively positioned farthest from and closest to the fixing unit. A distance between the first outlet and its corresponding photosensitive member is longer than a distance between the second outlet and its corresponding photosensitive member, whereas a distance between the first reflecting member and the polygonal mirror is shorter than a distance between the second reflecting member and the polygonal mirror.

This application is a division of application Ser. No. 16/575,651 filedSep. 19, 2019, currently pending; and claims priority under 35 U.S.C. §119 to Japan Application No. 2018-186516 filed on Oct. 1, 2018; and thecontents of all of which are incorporated herein by reference as if setforth in full.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image forming apparatus, such as acopying machine or a laser beam printer, using electrophotography.

As the image forming apparatus using electrophotography, an imageforming apparatus in which photosensitive members and developing deviceswhich correspond to four colors of yellow (Y), magenta (M), cyan (C) andblack (K) are arranged substantially in a straight line has been known.An image to forming apparatus disclosed in Japanese Laid-Open PatentApplication (JP-A) 2011-112705 is provided with cartridges 151Y, 151M,151C and 151K for the associated colors of Y, M, C and K, respectively,each in which the photosensitive member and the developing device areintegrally assembled into a unit as shown in FIG. 5 . Above thesecartridges 151Y, 151M, 151C and 151K, a single optical scanningapparatus 152 for irradiating the respective photosensitive members withlight beams is provided. A recording material passed through a fixingdevice 155 as an image heating portion is discharged onto a stackingtray 156.

Further, in an image forming apparatus shown in FIG. 8 , an opticalscanning apparatus 152 is constituted in the following manner. Theoptical scanning apparatus 152 deflects a light beam from a light sourceby a single deflector 153, so that photosensitive members of cartridges151Y, 151M, 151C and 151K are scanned with light beams through aplurality of deflecting (reflecting) mirrors 154Y, 154M, 154C and 154K.Further, in the image forming apparatus, a stacking tray 156 for stakinga recording material which passes through a fixing device 155 as theimage heating portion and which is to be discharged thereon is providedabove the optical scanning apparatus 152.

An image forming apparatus disclosed in JP-A 2005-91966 is provided witha single optical scanning apparatus 162 for irradiating a pluralityphotosensitive members 161Y, 161M, 161C and 161K which are juxtaposed,with light beams are provided below the photosensitive members as shownin FIG. 6 . The optical scanning apparatus 162 deflects a light beamfrom a light source by a single reflector 163, so that thephotosensitive members 161Y, 161M, 161C and 161K are scanned with lightbeams through a plurality of deflecting mirrors 164Y, 164M, 164C and164K. Further, in the image forming apparatus, a stacking tray 166 forstaking a recording material which passes through a fixing device 165 asthe image heating portion and which is to be discharged thereon isprovided at an upper portion of the image forming apparatus.

An image forming apparatus disclosed in JP-A 2006-30912 is provided witha single optical scanning apparatus 172 for irradiating a pluralityphotosensitive members 171Y, 171M, 171C and 171K which are juxtaposed,with light beams are provided above the photosensitive members as shownin FIG. 7 . The optical scanning apparatus 172 deflects a light beamfrom a light source by a single reflector 173, so that thephotosensitive members 171Y, 171M, 171C and 171K are scanned with lightbeams through a plurality of deflecting mirrors 174Y, 174M, 174C and174K. Further, in the image forming apparatus, a stacking tray 176 forstaking a recording material which passes through a fixing device 175 asthe image heating portion and which is to be discharged thereon isprovided above the optical scanning apparatus 172.

However, in the above-described image forming apparatuses disclosed inJP-A 2011-112705, JP-A 2005-91966 and JP-A 2006-30912, for convenienceof the optical scanning apparatuses, there arose a problem such that aheight of a main assembly of the image forming apparatus becomes large.

Particularly, the optical scanning apparatuses of the types of JP-A2011-112705 and JP-A 2006-30912 are required that the deflecting(reflecting) mirror is disposed above the photosensitive member for thecolor (yellow in JP-A 2011-112705) closest to the fixing device as theimage heating portion. In that case, when the stacking tray having aninclined surface such that a level on the image heating portion side islow is disposed so as to avoid the deflecting mirror, the height of themain assembly of the image forming apparatus has to be increased.

Therefore, a principal object of the present invention is to provide animage forming apparatus in which an inside space thereof is effectivelyutilized.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided animage forming apparatus comprising: a plurality of photosensitivemembers; a scanner unit configured to scan the photosensitive memberswith laser beams in accordance with image information, wherein thescanner unit includes light sources corresponding to the photosensitivemembers, respectively, a rotatable polygonal mirror configured toreflect and deflect the laser beams emitted from the light sources, anda plurality of reflecting members configured to reflect the laser beams,respectively, reflected by the rotatable polygonal mirror; and a fixingportion configured to fix, on a recording material, toner images formedon the photosensitive members and then superposed on the recordingmaterial, wherein parts of the laser beams emitted from the lightsources are reflected by the rotatable polygonal mirror toward a sidewhere the fixing device is provided, and rest parts of the laser beamsare reflected by the rotatable polygonal mirror toward a side oppositefrom the side where the fixing device is provided, wherein of the partsof the laser beams reflected by the rotatable polygonal mirror towardthe side where the fixing device is provided, the laser beam reflectedtoward the reflecting member provided at a position remotest from therotatable polygonal mirror travels downward relative to a horizontaldirection, and wherein a rotational axis of the rotatable polygonalmirror is inclined relative to a vertical direction.

According to another aspect of the present invention, there is providedan image forming apparatus comprising: a plurality of photosensitivemembers; a scanner unit configured to scan the photosensitive memberswith laser beams in accordance with image information, wherein thescanner unit includes light sources corresponding to the photosensitivemembers, respectively, a rotatable polygonal mirror configured toreflect and deflect the laser beams emitted from the light sources, anda plurality of reflecting members configured to reflect the laser beams,respectively, reflected by the rotatable polygonal mirror; and a fixingportion configured to fix, on a recording material, toner images formedon the photosensitive members and then superposed on the recordingmaterial, wherein parts of the laser beams emitted from the lightsources are reflected by the rotatable polygonal mirror toward a sidewhere the fixing device is provided, and rest part of the laser beamsare reflected by the rotatable polygonal mirror toward a side oppositefrom the side where the fixing device is provided, wherein of the partsof the laser beams reflected by the rotatable polygonal mirror towardthe side where the fixing device is provided, the laser beam reflectedtoward the reflecting member provided at a position remotest from therotatable polygonal mirror travels downward relative to an arrangementdirection of the photosensitive members, and wherein a rotational axisof the rotatable polygonal mirror is inclined relative to a directionperpendicular to the arrangement direction of the photosensitivemembers.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an image forming apparatus accordingto an embodiment 1.

FIG. 2 is a sectional view of an optical scanning apparatus according tothe embodiment 1.

FIG. 3 is a sectional view of an incident optical system toward apolygonal mirror of the optical scanning apparatus according to theembodiment 1.

FIG. 4 is a schematic sectional view of the optical scanning apparatusaccording to the embodiment 1.

FIG. 5 is a sectional view for illustrating a conventional image formingapparatus.

FIG. 6 is a sectional view for illustrating a conventional image formingapparatus.

FIG. 7 is a sectional view for illustrating a conventional image formingapparatus.

FIG. 8 is a sectional view for illustrating a conventional image formingapparatus.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be specifically described withreference to the drawings. Dimensions, materials, shapes and relativearrangements of constituent elements described in the followingembodiments should be appropriately be changed depending on structuresand various conditions of apparatuses to which the present invention isapplied. Accordingly, the scope of the present invention is not intendedto be limited to the following embodiments unless otherwise specified.

Embodiment 1

(Image Forming Apparatus)

With reference to FIG. 1 , an image forming apparatus according to anembodiment 1 will be described. FIG. 1 is a sectional view showing alaser beam printer which is an image forming apparatus 100 of thisembodiment. In the following, a general structure and function of thislaser beam printer will be described. In the following description, asregards the image forming apparatus 100, a front side is a side where aprocess cartridge PK is provided. A rear side is a side where a processcartridge PY is provided. A front-rear direction includes a direction(frontward direction) from the rear side toward the front side of theimage forming apparatus and a direction (rearward direction) opposite tothe frontward direction.

Inside the image forming apparatus 100, from the front side toward therear side, first to fourth (four) portions PY, PM, PC and PK arearranged and disposed substantially in the horizontal direction (inlineconstitution), tandem type). The four process cartridges in thisembodiment has a constitution in which the process cartridgescorresponding to four colors of yellow (Y), magenta (M), cyan (C) andblack (K) in a named order from the rear side toward the front side.Each of the process cartridges in this embodiment is prepared byintegrally assembling a photosensitive drum 11 as a photosensitivemember (image bearing member) and a developing roller 12 or the like asa process means actable on this drum into a unit. Further, each processcartridge also functions as a cartridge for accommodating toner. Of thefour process cartridges, the color of the toner accommodated in theprocess cartridge PK disposed at a position remotest from a fixingdevice 30 which is an image heating portion is black. Of the fourprocess cartridges, the process cartridge PK corresponding to blackdisposed on the forefront side is larger in toner volume than theprocess cartridges PY, PM and PC corresponding to other three colors.

Incidentally, here, as the cartridge, the process cartridge integrallyincluding the photosensitive member, the process means actable on thephotosensitive member, and a cartridge accommodating the toner wasdescribed as an example, but the present invention is not limitedthereto. For example, a constitution in which the cartridgeaccommodating the toner is provided separately from a process cartridgeintegrally including the photosensitive member and the process meansactable on the photosensitive member may also be employed.

Above these process cartridges PY, PM, PC and PK, an optical scanningapparatus 2 as an optical scanning portion is provided. This opticalscanning apparatus 2 scans a surface (surface-to-be-scanned) of thephotosensitive drum of each process cartridge with a light beam, so thatan electrostatic latent image is formed. In each process cartridge, theelectrostatic latent image formed on the photosensitive drum isdeveloped by the developing roller 12, so that a toner image is formedon the photosensitive drum.

Under the process cartridges PY, PM, PC and PK, an intermediary transferbelt unit 20 is provided. The intermediary transfer belt unit 20includes an intermediary transfer belt 21 which is an endless belt, anda plurality of stretching rollers consisting of a driving roller 22, atension roller 23 and a follower roller 24. The intermediary transferbelt 21 is stretched by the driving roller 22, the tension roller 23 andthe follower roller 24, and is rotated in an arrow direction in FIG. 1 .The photosensitive drums 11 of the process cartridges contact an uppersurface of the intermediary transfer belt 21. Inside the intermediarytransfer belt 21, four primary transfer rollers 25 are provided opposedto the photosensitive drums 11 of the process cartridges. The primarytransfer rollers 25 (25 a, 25 b, 25 c, 25 d) successively transfersuperposedly the toner images from the opposing photosensitive drums 11(11 a, 11 b, 11 c, 11 d) onto the intermediary transfer belt 21. Towardthe driving roller 22, a secondary transfer roller 26 is contacted tothe intermediary transfer roller 21. The secondary transfer roller 26collectively transfers the toner images from the intermediary transferbelt 21 onto the recording material.

At an upper portion of an inside of the image forming apparatus on therear side, the fixing device 30 which is an image heating portion forheating the image formed on the recording material and a dischargingdevice 40 which is a to discharging portion are provided. At an uppersurface of the image forming apparatus, a stacking tray 50 for stackingthe recording materials on which the images are formed is provided. Asthe fixing device 30, a fixing device including a fixing film 31 and apressing roller 32 is used. The discharging device 40 includesdischarging rollers 41 and 42 and discharges, toward the stacking tray50, the recording material passed through the fixing device 30.

The stacking tray 50 is disposed above the optical scanning apparatus 2.Sheets S which are the recording materials stacked in a feeding tray 61of a feeding device 60 are fed by a feeding roller 62 rotating in anarrow direction in FIG. 1 , and multi-fed sheets are separated and fedby a separate roller 63. Then, the sheet S is sent to a nip between thedriving roller 22 and the secondary transfer roller 26, and the tonerimages formed on the intermediary transfer belt 21 are transferred ontothe sheet S sent to the nip between the driving roller 22 and thesecondary transfer roller 26. Further, the sheet S on which the tonerimages are transferred is sent to a nip between the fixing film 31 andthe pressing roller 32 and is heated and pressed in the nip, so that thetoner images are fixed on the sheet S. The sheet S on which the tonerimages are fixed is discharged onto the discharge tray 50 by thedischarging rollers 41 and 42.

Here, in the image forming apparatus, the process cartridges PY, PM, PCand PK are arranged substantially in a line, but for the reason suchthat the process cartridge PK for black of the four colors is also usedin monochromatic printing or the like, a user amount of the black toneris larger than those of other toners of the three colors. Therefore, inorder to realize downsizing of the image forming apparatus whilereducing an exchange frequency of the process cartridge, it is affectiveto make only a black toner volume larger than other color toner volumes.

The exchange of the process cartridge is made by opening a front cover90 through rotation motion of the front cover 90 as shown by an arrow R1and then by pulling out the process cartridge toward the front side of amain assembly of the image forming apparatus (in an arrow U direction).Therefore, the process cartridge PK larger in volume and height thanother process cartridges can effectively utilize an inside space and candownsize the image forming apparatus when the process cartridge PK is ina forefront side of the main assembly (when being pulled out).

Further, the stacking tray 50 is disposed at the upper portion of theoptical scanning apparatus 2 as described above. The stacking tray 50 isinclined downward toward the fixing device 30 relative to a horizontalsurface in order to improve a positioning and orientation property ofdischarged sheets. The optical scanning apparatus 2 is obliquelydisposed in a direction in which a rear-side upper portion 13 of theoptical scanning apparatus 2 extends along inclination (inclined surface51) of the stacking tray 50. By disposing the stacking tray 50 in thismanner, the inside space of the image forming apparatus on a side belowthe stacking tray 50 is effectively utilized, so that the height of theimage forming apparatus can be suppressed to a low level.

Further, the stacking tray 50 disposed above the optical scanningapparatus 2 is formed in the following shape.

The stacking tray 50 has the inclined surface 51 inclined downwardlytoward the fixing device 30 from between a reflection mirror 10 c whichis a first reflecting member and a polygonal mirror 4 which is arotatable polygonal mirror, which are included in the optical scanningapparatus 2 as shown in FIG. 2 . The stacking tray 50 has a flat surface52 extending in a horizontal direction from between the reflectionmirror 10 c (first reflecting member) and the polygonal mirror 4(rotatable polygonal mirror) toward a side remote from the fixing device30. The inclined surface 51 has a constitution in which the recordingmaterial slides (moves) toward the discharging roller side in order toestablish positioning and orientation among the discharged recordingmaterials and to stack the recording materials on the stacking tray 50and in which end portions of the recording materials are thus positionedand oriented by a wall of the image forming apparatus. Incidentally, inthis embodiment, the flat surface 52 of the stacking tray 50 is providedon the front side of the image forming apparatus, but the presentinvention is not limited thereto and the surface of the stacking tray 50on the front side may also be a moderately curved surface.

Further, the stacking tray 50 has the inclined surface 51 just above arotation center of the photosensitive drum 11 a closest to the fixingdevice 30. The stacking tray 50 has the flat surface 52 just above arotation center of the photosensitive drum 11 d remotest from the fixingdevice 30. As shown in FIG. 4 , a crossing portion 53 where the inclinedsurface 51 and the flat surface 52 of the stacking tray 50 cross eachother is positioned, with respect to the horizontal direction, betweenrotation centers of the two photosensitive drums 11 b and 11 c close tothe polygonal mirror 4 (rotatable polygonal mirror). In FIG. 4 , avertical line from the rotation center of one photosensitive drum 11 bclose to the polygonal mirror 4 is represented by X2, a vertical linefrom the rotation center of the other photosensitive drum 11 c close tothe polygonal mirror 4 is represented by X3. The crossing portion 53where the inclined surface 51 and the flat surface 52 of the stackingtray 50 cross each other is positioned between the vertical line X2 andthe vertical line X3.

A relationship in height with respect to a vertical direction between arecording material stacking surface of the stacking tray 50 and adischarge opening 43 through which the recording material is to bedischarged onto the stacking tray 50 as follows. The stacking tray 50includes, as the recording material stacking surface, the inclinedsurface 51 and the flat surface 52. As shown in FIG. 4 , a first pointof intersection between the vertical line X2 passing through therotation center of the photosensitive drum 11 a closest to the fixingdevice 30 and the stacking tray 50 (inclined surface 51) is a firstposition 51 a. A second point of intersection between the vertical lineX3 passing through the rotation center of the photosensitive drum 11 dremotest from the fixing device 30 and the stacking tray 50 (flatsurface 52) is a second position 52 a.

A shape of the stacking tray 50 is such that a relationship in heightamong the discharge opening 43, the first position 51 a of the stackingtray 50 and the second position 52 a of the stacking tray 50 satisfy:(first position 51 a of stacking tray 50)<(discharge opening 43)<(secondposition 52 a of stacking tray 50).

Further, light beams L1, L2, L3 and L4 emitted from the optical scanningapparatus 2 and incident on the photosensitive drums 11 a, 11 b, 11 cand 11 d are obliquely incident on the respective photosensitive drumsfrom a side opposite from the fixing device 30 side with respect to avertical direction of the image forming apparatus. As a result, comparedwith the case where the light beams are caused to be incident on thephotosensitive drums in the vertical direction, the optical scanningapparatus 2 can be disposed on the front side of the image formingapparatus, so that it is possible to avoid interference between therear-side upper portion 13 of the optical scanning apparatus 2 and theinclined surface 51 of the stacking tray 50, and thus the height of theimage forming apparatus can be suppressed to a low level. In thisembodiment, the light beams are caused to be incident on thephotosensitive drums by being inclined relative to vertical lines X1,X2, X3 and X4 by 10°.

Next, the optical scanning apparatus 2 will be described with referenceto FIGS. 2 and 3 . FIG. 2 is a sectional view of the optical scanningapparatus 2 in this embodiment, and is the sectional view of an opticalscanning system in which the light beams deflected by the polygonalmirror are guided to the photosensitive drums. FIG. 3 is a sectionalview of an incident optical system on the polygonal mirror of theoptical scanning apparatus.

The optical scanning apparatus 2 according to this embodiment is, asshown in FIG. 2 , an optical scanning portion for scanning the pluralityof photosensitive drums with the light beams, emitted from the pluralityof light sources, through optical members by the polygonal mirror 4which is the rotatable polygonal mirror includes in the deflector. Inthe optical scanning apparatus 2 shown in FIG. 2 , the optical membersillustrated are first imaging lenses 8 which are first imaging members,second imaging lenses 9 which are second imaging members, and reflectionmirrors 10 a, 10 b, 10 c, 10 d, 10 e and 10 f which are reflectingmembers. The deflector includes the polygonal mirror 4 which is therotatable polygonal mirror. The optical scanning apparatus 2 includesthe deflector including the polygonal mirror 4, the imaging lenses 8 and9, the reflection mirrors 10 a-10 f, and a frame 2 a to which thesemembers are mounted. The deflector including the polygonal mirror 4 ismounted on the frame 2 a on an upper surface side. In the opticalscanning apparatus 2, these optical members are disposed in abilaterally asymmetrical manner between a scanning region A1 and ascanning region A2 with respect to the polygonal mirror 4. Here, thescanning region A1 is a first region on the fixing device 30 side (imageheating portion side) and is a region in which the light beams L1 and 12incident on the photosensitive drums 11 a and 11 b pass. The scanningregion A2 is a second region on an opposite side (opposite image heatingportion side) from the fixing device 30 side and is a region in whichthe light beams L3 and L4 incident on the photosensitive drums 11 c and11 d pass. The optical scanning apparatus 2 deflects the light beams L1,L2, L3 and L4 emitted from the plurality of light sources in a divisionmanner into the scanning region A1 on the fixing device 30 side and thescanning region A2 on the opposite side from the fixing to device 30 bythe polygonal mirror 4. Of the reflecting members of the opticalscanning apparatus 2, the reflection mirror 10 c is a first reflectingmember disposed at a position remotest from the polygonal mirror 4 inthe scanning region A1 which is the first region and reflecting, towardthe photosensitive drum 11 a, the light beam L1 reflected toward thescanning region A1. Further, the reflection mirror 10 f is a secondreflecting member disposed at a position remotest from the polygonalmirror 4 in the scanning region A2 which is the second region andreflecting, toward the photosensitive drum 11 d, the light beam L4reflected toward the scanning region A2.

The optical scanning apparatus 2 is disposed such that an axis of thepolygonal mirror 4 is inclined relative to the vertical direction sothat the image heating portion side is lower than the opposite imageheating portion side with respect to a horizontal line (rectilinear lineY). Here, in the image forming apparatus 100 of this embodiment, ahorizontal direction refers to a direction of the rectilinear line Yconnecting rotation centers of the remotest two develops 11 a and 11 dof the four photosensitive drums. Further, the deflector including thepolygonal mirror 4 is disposed at a position close to the photosensitivedrum 11 c relative to an intermediary point CH between the twophotosensitive drums 11 b and 11 c. That is, the deflector is disposedat the position, with respect to the horizontal direction, closer to thephotosensitive drum 11 b disposed on the opposite image heating portionside than to the photosensitive drum 11 b disposed on the image heatingportion side, in which the two photosensitive drums 11 b and 11 c aredisposed while sandwiching the deflector therebetween and are closest tothe deflector. Thus, the polygonal mirror 4 is inclined relative to thehorizontal direction, whereby the optical scanning apparatus 2 can bedisposed obliquely relative to the horizontal direction in the imageforming apparatus. Further, in the horizontal direction, the position ofthe polygonal mirror 4 is brought nearer to the photosensitive drum 11 cthan to the photosensitive drum 11 b, so that even when the polygonalmirror 4 is inclined from the horizontal direction, lengths of the lightbeams L1, L2, L3 and L4 can be kept at the same length. Incidentally,the intermediary point CH is also an intermediary point between therotation centers of the photosensitive drums 11 a and 11 d. Accordingly,a vertical line XC passing through the intermediary point CH shown inFIG. 2 is a vertical line equidistant from the vertical line X1 passingthrough the rotation center of the photosensitive drum 11 a and avertical line X4 passing through the rotation center of thephotosensitive drum 11 b. With respect to this vertical line XC, thevertical line X1 side is the image heating portion side, and thevertical line X4 side is the opposite image heating portion side whichis a side opposite from the image heating portion side.

In this embodiment, a so-called an oblique incident optical system isemployed. The oblique incident optical system is, as shown in FIG. 3 ,an optical system such that the light beams L1 and L2 are caused to beobliquely incident on a plane D perpendicular to a rotational axis C ofthe polygonal mirror 4. Incident optical systems each consisting of alight source portion 3 which is a light source, a collimator lens 5 anda cylindrical lens 6 are vertically arranged with respect to the plane Dperpendicular to the rotational axis C, and the light beams are causedto be incident on the reflecting surface 7 of the polygonal mirror 4with desired angles θ with respect to the plane D perpendicular to thereflecting surface 7, so that these incident optical systems aresymmetrical with respect to the plane D. Of the plurality of lightsources shown in FIG. 2 , the light source portion 3 on a side above theplane D is a first light source provided being inclined with respect tothe plane D by the desired angle θ. The light beam L1 emitted from theupper-side light source portion 3 is incident on the reflecting surface7 of the polygonal mirror 4 from an obliquely upper side in the angle θ.The light beam L1 emitted, by the upper-side light source portion 3,from the obliquely upper side with respect to the plane D toward thereflecting surface 7 of the polygonal mirror 4 is reflected by thereflecting surface 7 of the polygonal mirror 4 toward the scanningregion A1 shown in FIG. 2 and toward an obliquely lower side withrespect to the plane D. On the other hand, the light source portion 3 ona side below the plane D is a second light source provided beinginclined with respect to the plane D by the desired angle θ. The lightbeam L2 emitted from the lower-side light source portion 3 is incidenton the reflecting surface 7 of the polygonal mirror 4 from an obliquelylower side in the angle θ. The light beam L2 emitted, by the lower-sidelight source portion 3, from the obliquely lower side with respect tothe plane D toward the reflecting surface 7 of the polygonal mirror 4 isreflected by the reflecting surface 7 of the polygonal mirror 4 towardthe scanning region A1 shown in FIG. 2 and toward an obliquely upperside with respect to the plane D. Thus, the light beams L1 and L2 fromthe upper and lower (two) light source portions 3 are caused to beincident on the reflecting surface 7 from obliquely upper and lowersides, respectively, so that the light beams L1 and L2 are separable inupper and lower optical paths after being reflected by the polygonalmirror 4.

Incidentally, although not illustrated in FIG. 3 , the incident opticalsystem including the light sources for emitting the light beams L3 andL4 also employs a similar constitution. That is, the light beams L3 andL4 from the upper and lower (two) light sources 3 are caused to beincident on the reflecting surface 7 from the obliquely upper and lowersides, respectively, so that the light beams L3 and L4 are separable inupper and lower optical paths after being reflected by the polygonalmirror 4. The light beam L3 emitted by the upper side light sourceportion 3 toward the reflecting surface 7 of the polygonal mirror 4 fromthe obliquely upper side relative to the plane D is reflected by the toreflecting surface 7 of the polygonal mirror 4 toward the scanningregion A2 shown in FIG. 2 and toward the obliquely lower side relativeto the plane D. The light beam L4 emitted by the lower-side light sourceportion 3 toward the reflecting surface 7 of the polygonal mirror 4 fromthe obliquely lower side relative to the plane D is reflected by thereflecting surface 7 of the polygonal mirror 4 toward the scanningregion A2 shown in FIG. 2 and toward the obliquely upper side relativeto the plane D.

Next, referring to FIG. 2 again, the optical scanning apparatus 2 inthis embodiment will be described. The light beams L1 and L2 allocatedto the scanning region A1 which is the first region and the light beamsL3 and L4 allocated to the scanning region A2 which is the second regionwill be described in a named order.

The light beams incident on the reflecting surface 7 of the polygonalmirror 4 are reflected with the angle θ relative to the plane Dperpendicular to the rotational axis C of the polygonal mirror 4.

First, on the scanning region A1 side, the two light beams L1 and L2reflected by the reflecting surface 7 are incident on a first imaginglens 8 which is a first imaging member common to the light beams L1 andL2.

Of the light beams coming out of the first imaging lens 8, the outgoinglight beam L2 toward the obliquely upper side relative to the plane Dperpendicular to the rotational axis C is reflected by a firstreflection mirror 10 a. Thereafter, the light beam L2 is reflected againby a second reflection mirror 10 b and passes through a second imaginglens 9 and then reaches the photosensitive drum 11 b.

Of the light beams coming out of the first imaging lens 8, the outgoinglight beam L1 toward the obliquely lower side relative to the plane Dperpendicular to the rotational axis C passes blow the first reflectionmirror 10 a to and is reflected by a third reflection mirror 10 c, andthereafter passes through a second imaging lens 9 and then reaches thephotosensitive drum 11 a. Here, the third reflection mirror 10 c of thereflecting members of the optical scanning apparatus 2 is a firstreflecting member which is disposed at a position remotest from thepolygonal mirror 4 in the scanning region A1 being the first region andwhich reflects the light beam L1 toward the photosensitive drum 11 a.The light beam L1 reflected by the reflecting surface 7 of the polygonalmirror 4 toward the scanning region A1 and the obliquely lower siderelative to the plane D as described above, and thereafter is reflectedonly by the above-described reflection mirror 10 c which is the firstreflecting member until the light beam L1 reaches the photosensitivedrum 11 a.

The first imaging lens 8 is shared between the light beams L1 and L2,and the second imaging lens 9 is provided for each of the light beams L1and L2.

On the other hand, on the scanning region A2 side, the two light beamsL3 and L4 reflected by the reflecting surface 7 are incident on a firstimaging lens 8 which is a first imaging member common to the light beamsL3 and L4.

Of the light beams coming out of the first imaging lens 8, the outgoinglight beam L3 toward the obliquely lower side relative to the plane Dperpendicular to the rotational axis C is reflected by a fourthreflection mirror 10 d. Thereafter, the light beam L3 is reflected againby a fifth reflection mirror 10 e and passes through a second imaginglens 9 and then reaches the photosensitive drum 11 c.

Of the light beams coming out of the first imaging lens 8, the outgoinglight beam L4 toward the obliquely upper side relative to the plane Dperpendicular to the rotational axis C passes above the fourthreflection mirror 10 d and is reflected by a sixth reflection mirror 10f, and thereafter passes through a second imaging lens 9 and thenreaches the photosensitive drum 11 d. Here, the sixth reflection mirror10 f of the reflecting members of the optical scanning apparatus 2 is asecond reflecting member which is disposed at a position remotest fromthe polygonal mirror 4 in the scanning region A2 being the first regionand which reflects the light beam L4 toward the photosensitive drum 11d. The light beam L4 reflected by the reflecting surface 7 of thepolygonal mirror 4 toward the scanning region A2 and the obliquely upperside relative to the plane D as described above, and thereafter isreflected only by the above-described reflection mirror 10 f which isthe first reflecting member until the light beam L4 reaches thephotosensitive drum 11 d.

Similarly as the scanning region A1, also on the scanning region A2side, the first imaging lens 8 is shared between the light beams L3 andL4, and the second imaging lens 9 is provided for each of the lightbeams L3 and L4.

On the scanning region A1 side, as described above, the upper light beamL2 relative to the plane D perpendicular to the rotational axis C isseparated from the lower light beam L1 with use of the reflection mirror10 a, and is guided to the photosensitive drum 11 b on the polygonalmirror 4 side. Further, the lower light beam L1 relative to the plane Dperpendicular to the rotational axis C is guided to the photosensitivedrum 11 a on the image heating portion side with use of the reflectionmirror 10 c which is the first reflecting member. The reflection mirror10 c which is the first reflecting member is disposed at the position(on the image heating portion side in this embodiment) remotest from thepolygonal mirror 4 as described above. Thus, the upper light beam L2 isseparated using the reflection mirror at the position close to thepolygonal mirror 4 on the scanning region A1 side which is the imageheating portion side. As a result, a narrow space between the processcartridge PY and a lower portion, on the opposite image heating portionside, of the stacking tray 50 including the inclined surface 51 suchthat the image heating portion side is lower than the opposite imageheating portion side can be effectively utilized. Incidentally, a rangeof a portion under the stacking tray 50 on the image heating portionside is an overlapping range, with respect to the vertical direction,between the scanning region A1 of the optical scanning apparatus 2 onthe image heating portion side and a region on the vertical line X1 side(image heating portion side) with respect to the vertical line XC.

On the other and, on the scanning region A2 side, contrary to the abovecase, the lower light beam L3 relative to the plane D perpendicular tothe rotational axis C is separated from the upper light beam L3 with useof the reflection mirror 10 d, and is guided to the photosensitive drum11 b on the polygonal mirror 4 side. Further, the upper light beam L4relative to the plane D perpendicular to the rotational axis C is guidedto the photosensitive drum 11 d on the opposite image heating portionside with use of the reflection mirror 10 f which is the secondreflecting member. The reflection mirror 10 f which is the secondreflecting member is disposed at the position (on the opposite imageheating portion side in this embodiment) remotest from the polygonalmirror 4 as described above. Thus, the lower light beam L3 is separatedusing the reflection mirror 10 d at the position close to the polygonalmirror 4 on the scanning region A2 side which is the opposite imageheating portion side. As a result, a space above the process cartridgePk on the forefront side (opposite image heating portion side) can bebroadly ensured.

Further, as described above, the optical scanning apparatus 2 isdisposed such that the axis of the polygonal mirror 4 is inclinedrelative to the vertical direction so that the image heating portionside is lower than the opposite image heating portion side. Further, inthe optical scanning apparatus 2, the light beam L1 reflected by thereflecting surface 7 of the polygonal mirror 4 toward the scanningregion A1 shown in FIG. 2 and toward the obliquely lower side relativeto the plane D is reflected toward the photosensitive drum 11 a by thereflection mirror 10 c. Further, in the optical scanning apparatus 2,the light beam L4 reflected by the reflecting surface 7 of the polygonalmirror 4 toward the scanning region A2 shown in FIG. 2 and toward theobliquely upper side relative to the plane D is reflected toward thephotosensitive drum 11 d by the reflection mirror 10 d. By thisconstitution, the optical scanning apparatus 2 is capable of beingchanged to various shapes with no bilateral symmetry with respect to theaxis of the polygonal mirror 4, so that the shape of the opticalscanning apparatus 2 can be formed depending on an outer casing of theimage forming apparatus. As a result, the space inside the image formingapparatus can be effectively utilized.

Further, by employing the above-described arrangement constitution ofthe reflecting members of the optical scanning apparatus 2, a distancebetween an emergent opening remotest from the fixing device 30 and thephotosensitive drum corresponding to the emergent opening is longer thandistances each between another emergent opening and an associatedphotosensitive drum. A relationship of these distances is shown in FIG.4 . FIG. 4 is a schematic sectional view of the optical scanningapparatus 2 in this embodiment. As shown in FIG. 4 , the distancebetween an emergent opening 14 d remotest from the fixing device 30 andthe photosensitive drum 11 d corresponding to the emergent opening 14 dis longer than the distance between other emergent openings 14 a, 14 band 14 c and the photosensitive drums 11 a, 11 b and 11 c, respectively.Specifically, a distance Ld between the emergent opening 14 d remotestfrom the fixing device 30 and the photosensitive drum 11 d correspondingto the remotest emergent opening 14 d is longer than a distance Labetween the emergent opening 14 a closest to the fixing device 30 andthe photosensitive drum 11 a corresponding to the closest emergentopening 14 a. Incidentally, a relationship among distances La, Lb, Lcand Ld between the emergent openings 14 a, 14 b, 14 c and 14 d and thecorresponding photosensitive drums 11 a, 11 b, 11 c and 11 d,respectively, is La=Lb=Lc<Ld. Further, a distance ha from the rotationcenter of the photosensitive drum 11 a, closest to the fixing device 30,to the stacking tray 50 (inclined surface 51) with respect to thevertical direction is shorter than a distance hd from the rotationcenter of the photosensitive drum 11 d, remotest from the fixing device30, to the stacking tray 50 (flat surface 52) with respect to thevertical direction. As a result, a space between a lower portion of thestacking tray 50 on the image heating portion side and the processcartridge PY disposed on the image heating portion side closest to thefixing device 30 can be effectively utilized. At the same time, a spaceabove the process cartridge PK on the forefront side (opposite imageheating portion side) can be broadly ensured.

According to this embodiment, the space between the lower portion of thestacking tray on the image heating portion side and the processcartridge disposed on the image heating portion side closest to thefixing device can be utilized effectively. At the same time, also thespace above the process cartridge (the black process cartridge increasedin volume in this embodiment) disposed on the opposite image heatingportion side remotest from the fixing device can be utilizedeffectively. As a result, it is possible to realize an image formingapparatus in which the inside space is effectively utilized.

OTHER EMBODIMENTS

In the above-described embodiment, as a constitution in which thephotosensitive member is scanned with the light beam, deflected by thedeflector, through the optical members, a constitution in which thephotosensitive member is scanned with the light beam through the twoimaging lenses was described as an example, but the present invention isnot limited thereto, and a single imaging lens or three or more imaginglenses may also be used. Further, a constitution of a single reflectionmirror or two reflection mirrors was also described as an example, butthe present invention is not limited thereto, and may only be requiredto be appropriately set.

In the above-described embodiment, the case where the relationship ofthe distances La, Lb, Lc and Ld between the emergent openings 14 a, 14b, 14 c and 14 d of the optical scanning apparatus 2 and thecorresponding photosensitive drums 11 a, 11 b, 11 c and 11 d isLa=Lb=Lc<Ld was described as an example. However, the relationship ofthe distances La, Lb, Lc and Ld is not limited thereto. Of the distancesLa, Lb and Lc and Ld, compared with the distances La and Lb, thedistances Lc and Ld may be long, and the distances Lc and Ld may also beequal to each other. Also by this constitution, similarly as in theabove-described embodiment, the space between the lower portion of thestacking tray on the image heating portion side and the processcartridge disposed on the image heating portion side can be effectivelyutilized. At the same time, the space above the process cartridgedisposed on the opposite image heating portion side can be broadlyensured.

In the above-described embodiment, the four process cartridges wereused, but the number of the process cartridges used is not limitedthereto, and may only be required to be appropriately set as desired.

Further, in the above-described embodiment, the constitution in whichthe process cartridges are supported so as to be mountable in anddismountable from the supporting member pulled out from the rear sidetoward the front side of the image forming apparatus was described as anexample, but the present invention is not limited thereto. Aconstitution in which the process cartridges are directly mounted in anddismounted from the image forming apparatus may also be employed.

Further, in the above-described embodiment, the constitution in whichthe process cartridge including the photosensitive member, the processmeans and the cartridge accommodating the toner is mountable in anddismountable from the image forming apparatus was described as anexample, but the present invention is not limited thereto. For example,an image forming apparatus in which respective constituent elements,constituting a cartridge, such as the photosensitive member, the processmeans and the toner cartridge are mountable in and dismountable from theimage forming apparatus may also be employed.

Further, in the above-described embodiment, as the image formingapparatus, the printer was described as an example, but the presentinvention is not limited thereto. For example, other image formingapparatuses such as a copying machine, a facsimile apparatus or otherimage forming apparatuses such as a multi-function machine havingfunctions of these machines in combination may also be used. Further,the present invention is not limited to the image forming apparatus inwhich the intermediary transfer belt which is the intermediary transfermember is used and the toner images of the respective colors aresuccessively transferred superposedly onto the intermediary transfermember and then are collectively transferred onto the recordingmaterial. For example, an image forming apparatus in which a recordingmaterial carrying member is used and the toner images of the respectivecolors are successively transferred superposedly onto a recordingmaterial carried on the recording material carrying member may also beused. By applying the present invention to these image formingapparatuses, a similar effect can be obtained.

Further, in the above-described embodiment, the horizontal direction isthe direction of the rectilinear line Y connecting the rotation centersof the photosensitive drums 11 a and 11 d, of the four photosensitivedrums, remotest from each other, but the present invention may also beapplied to an image to forming apparatus in which the horizontaldirection and the rectilinear line Y are non-parallel with each other.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2018-186516 filed on Oct. 1, 2018, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image forming apparatus comprising: aplurality of photosensitive members; a scanner unit configured to scansaid photosensitive members with laser beams in accordance with imageinformation, wherein said scanner unit includes light sourcescorresponding to said photosensitive members, respectively, a rotatablepolygonal mirror configured to reflect and deflect the laser beamsemitted from said light sources, reflecting members configured toreflect the laser beams reflected by said rotatable polygonal mirror,and a box configured to accommodate said rotatable polygonal mirror andsaid reflecting members; a fixing unit configured to fix, on a recordingmaterial, toner images formed on said photosensitive members and thensuperposed on the recording material, and a discharge tray configured toreceive the recording material on which the images are formed and whichis discharged from an inside of said image forming apparatus, whereinsaid scanner unit is provided between said plurality of photosensitivemembers and said discharge tray with respect to a vertical direction,wherein said box includes a plurality of outlets for emitting the laserbeams corresponding to said photosensitive members, respectively,wherein selected ones of the laser beams emitted from said light sourcesare reflected by said rotatable polygonal mirror toward a side wheresaid fixing unit is provided, and remaining ones of the laser beams arereflected by said rotatable polygonal mirror toward a side opposite fromthe side where said fixing unit is provided, wherein a distance betweenthe outlet farthest from said fixing unit and a correspondingphotosensitive member is longer than a distance between the outletclosest to said fixing unit and a corresponding photosensitive member,wherein said reflecting members include a first reflecting member forreflecting the laser beam reflected from said rotatable polygonal mirrortoward the outlet farthest from said fixing unit and a second reflectingmember for reflecting the laser beam reflected from said rotatablepolygonal mirror toward the outlet closest to said fixing unit, whereinin an optical path of the laser beam from said rotatable polygonalmirror to the outlet farthest from said fixing unit, only said firstreflecting member exists as a member that reflects the laser beam, andin an optical path of the laser beam from said rotatable polygonalmirror to the outlet closest to said fixing unit, only said secondreflecting member exists as a member that reflects the laser beam, andwherein a distance between said first reflecting member and saidrotatable polygonal mirror is shorter than a distance between saidsecond reflecting member and said rotatable polygonal mirror.
 2. Animage forming apparatus according to claim 1, wherein a rotational axisof said rotatable polygonal mirror is inclined relative to the verticaldirection.
 3. An image forming apparatus according to claim 1, whereinsaid discharge tray includes an inclined surface for receiving therecording material on which an image is formed and which is dischargedfrom an inside of said image forming apparatus, wherein said scannerunit overlaps with said inclined surface as seen in the verticaldirection.